Multi-core processor and method of communicating across a die

ABSTRACT

A multi-core die is provided that allows packets to be communicated across the die using resources of a packet switched network and a circuit switched network.

BACKGROUND

1. Field

Embodiments of the present invention may relate to a multi-coreprocessor.

2. Background

A multi-core processor may include two or more independent cores in asingle package composed of a single integrated circuit (IC), called die,or more dies packaged together. For example, a dual-processor maycontain two cores and a quad-processor may contain four cores. Themulti-core processor may implement multiprocessing in a single physicalpackage. A processor with all cores on a single die may be called amonolithic processor.

BRIEF DESCRIPTION OF THE DRAWINGS

Arrangements and embodiments may be described in detail with referenceto the following drawings in which like reference numerals refer to likeelements and wherein:

FIG. 1 shows a die having a plurality of cores that operate as apacket-switched network providing intra-die communication in accordancewith an example arrangement;

FIG. 2 shows a die having a plurality of cores that operate as a packetswitched network and a circuit switched network in accordance with anexample embodiment of the present invention;

FIG. 3 is a flowchart of a method of communicating data on a multi-coredie according to an example embodiment of the present invention; and

FIG. 4 shows a router of one core in accordance with an exampleembodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention may include an on-chip hybridinterconnect network system for a multi-core die to manage a powerbudget.

FIG. 1 shows a die having a plurality of cores that operate as apacket-switched network providing intra-die communication in accordancewith an example arrangement. Other arrangements may also be used.

More specifically, FIG. 1 shows a die 10 that includes a plurality ofcores 12, 22, 32, 42, 52, 62, 72, 82 and 92 mounted thereon. The die 10is therefore considered to be a multi-core die. The die 10 shows themulti-cores organized or arranged as a grid, although the cores may beorganized or arranged differently. The cores may be provided in anetwork or communicate in a network, such as a packet switched network,of the die 10.

The cores 12, 22, 32, 42, 52, 62, 72, 82 and 92 may be coupled togetherby interconnects 14, 16, 24, 26, 34, 44, 46, 54, 56, 64, 74 and 84. Morespecifically, the core 12 may be coupled to the core 22 by theinterconnect 14, and the core 12 may be coupled to the core 42 by theinterconnect 16. The core 22 may be coupled to the core 32 by theinterconnect 24, and the core 22 may be couple to the core 52 by theinterconnect 26. Still further, the core 32 may be coupled to the core62 by the interconnect 34.

The core 42 may be coupled to the core 52 by the interconnect 44, andthe core 42 may be coupled to the core 72 by the interconnect 46. Thecore 52 may be coupled to the core 62 by the interconnect 54, and thecore 52 may be coupled to the core 82 by the interconnect 56. Stillfurther, the core 62 may be coupled to the core 92 by the interconnect64. The core 72 may also be coupled to the core 82 by the interconnect74, and the core 82 may be coupled to the core 92 by the interconnect84.

In FIG. 1, packets may be communicated among the various cores usingresources of the packet switched network. That is, the packet switchednetwork may provide communication between the cores. The packets mayinclude a control portion and a data portion. The control portion mayinclude a destination address of the packet, and the data portion maycontain the specific data to be communicated on the die 10. For example,the control portion may include a destination address that correspondsto one of the cores of the die. The packet switched network may includebuffering because a dedicated path is not assured from a source to adestination and so a packet may need to be stopped temporarily if two ormore packets need to traverse a same link or interconnect.

In a packet switched network, the packets may be buffered at each of therespective cores as the packet travels from a source to a destination.The packets may be received, transmitted and processed in a router (notshown) of each core. For example, FIG. 1 shows two components of arouter within the core 62, namely a control portion component 62A and adata portion component 62B. Although, the components 62A and 62B areshown as separate elements of the router, the components 62A and 62B maybe provided as one component.

The control portion component 62A may include a plurality of flip-flops66 coupled in series to buffer the control portion of a packet as thepacket passes through the router of the core. The first one of theflip-flops 66 may receive the control portion of the packet from anotherrouter located at another core, and the last one of the flip-flops 66 ofone router may provide the control portion of the packet to anotherrouter (on another core).

The data portion component 62B may include a plurality of flip-flops 68coupled in series to buffer the data portion of a packet as the packetpasses through the router. The first one of the flip-flops 68 mayreceive the data portion of the packet from another router located atanother core, and the last one of the flip-flops 68 of the router mayprovide the data portion of the packet to another router (on another oneof the cores).

The packet switched network may buffer packets at each of the coresusing the flip-flops 66 and 68 in the components 62A and 62B. The packetswitched network may use point-to-point communication betweenneighboring cores. The control portions of the packets may betransferred between cores based on a packet clock, such as a 4 GHzclock. The data portion of the packets may be transferred between coresbased on a similar clock, such as a 4 GHz clock. While packet switchingoffers flexibility in routing, packet switching may suffer from largepower consumption associated with a necessity to buffer packets at eachcore.

FIG. 2 shows a die having a plurality of cores that operate as a packetswitched network and a circuit switched network in accordance with anexample embodiment of the present invention. Other embodiments andconfigurations are also within the scope of the present invention.

More specifically, FIG. 2 shows a die 100 that includes the plurality ofcores 12, 22, 32, 42, 52, 62, 72, 82 and 92 mounted thereon, and theplurality of interconnects 14, 16, 24, 26, 34, 44, 46, 54, 56, 64, 74and 84. For ease of illustration, the cores and the interconnects may bearranged and coupled on the die 100 in a similar manner as the die 10 inFIG. 1. The die 100 may therefore be considered a multi-core die. Thecores may be provided in two networks or communicate in two networks,such as a packet switched network and a circuit switched network, of thedie 100. Although not shown in FIG. 2, a router may be provided withineach of the cores 12, 22, 32, 42, 52, 62, 72, 82 and 92.

In FIG. 2, packets may be communicated among the various cores usingresources of the packet switched network and using resources of thecircuit switched network.

FIG. 2 shows two components of a router of the core 62, namely a controlportion component 62A and a data portion component 62C. Although notshown in FIG. 2, the router may also include the data portion component62B shown in FIG. 1 since resources within the component 62B may beconsidered resources of the packet switched network. FIG. 2 shows thecomponents 62A and 62C as separate elements of the router, although thecomponents 62A and 62C may be provided as one component.

The control portion component 62A may include the plurality offlip-flops 66 coupled in series to buffer the control portion of apacket as the packet passes through the router. In a similar manner asdiscussed above, the first one of the flip-flops 66 may receive thecontrol portion of the packet from another router (on another one of thecores), and the last one of the flip-flops 66 may provide the controlportion of the packet to another router (on another core).

The data portion component 62C may include a multiplexer 68 to receivethe data portion of packets from neighboring cores, and to provide thedata portion to another neighboring core. As such, the data portioncomponent 62C may not utilize the flip-flops 66 (from the packet switchnetwork). The circuit switched network may therefore avoid bufferingdata packets at each of the cores. Both the packet switched network andthe circuit switched network may use multiplexers.

The die 100 may communicate among the cores using resources of thepacket switched network and using resources of the circuit switchednetwork. For example, a control portion of a packet may be sent from asource core to a destination core without simultaneously sending thecorresponding data portion of the packet. The sending of the controlportion of a packet may utilize resources of the packet switchednetwork. Upon the control portion being received at the destinationcore, an acknowledgement signal (or message) may be sent from thedestination core to the source core by utilizing resources of thecircuit switched network. The source core may then send the data portionof the packet from the source core to the destination core by utilizingresources of the circuit switched network.

Because the die 100 utilizes resources of two networks, different clockspeeds may be used, which leads to less power consumption. For example,control portions of the packets may be transferred between cores of thedie 100 based on a packet clock, such as a 4 GHz clock, whichcorresponds to a packet switch clock. The data portion of the packetsmay be transferred between cores of the die 100 based on a different andslower clock, such as a 1 GHz clock, which corresponds to a circuitswitch clock.

As each control portion (or request) passes each core/interconnectsegment, the corresponding data channel for that segment (i.e., thecorresponding interconnect) may be allocated for the upcoming dataportion of the packet. Therefore, when the control portion reaches thedestination, a complete channel or circuit may have been established forthe upcoming data portion of the packet. This channel may utilize alatching or storage element only at the destination with multiplexersand repeaters (not shown explicitly) at each core (or node) along theway.

The destination core, upon receiving the control portion, may send asingle acknowledgement signal (or message) back to the source, therebyindicating that the destination is ready to receive the data. When thesource receives this acknowledgement signal, the source may drive thedata onto its output. The data may propagate from the source to thedestination without interruption by state elements along the path.

Different clocks may be used to synchronize the packet switched networkand the circuit switched network. Since each portion of the packettravels only between neighboring cores during each cycle, the die 100may operate with a higher frequency clock (packet clock) when utilizingresources of the packet switched network than the circuit switchednetwork (data clock), where data travels across the whole network eachcycle.

In order to transmit a single data packet, the circuit switched networkallocates an entire path whereas the packet switched network allocatesonly a single segment (or interconnect). This results in difference inthroughput. To compensate for this difference in throughput, a data bitwidth of the circuit switched network may be increased to result inequal throughput.

The die 100 that utilizes both the packet switched network and thecircuit switched network may not utilize nearly all state elements whenusing resources of the circuit switched network by latching the dataonly at the final destination. In the packet switched network, most ofthe power consumed by clocked state elements which may be used forpacket staging.

FIG. 3 is a flowchart of a method of communicating data on a multi-coredie according to an example embodiment of the present invention Otheroperations, orders of operations and embodiments are also within thescope of the present invention.

More specifically, FIG. 3 shows operations associated with sending datafrom a source core to a destination core by utilizing resources of boththe packet switched network and the circuit switched network. As anexample, FIG. 3 describes the sending of data from core 12 (i.e., thesource) to the core 52 (i.e., the destination). Other examples are alsowithin the scope of the present invention.

In operation 152, the core 12 may send a control portion of a packetacross the interconnect 14 to the core 22. In operation 154, the controlportion of the packet may pass through the core 22 and pass across theinterconnect 26 to the core 52 (i.e., the destination).

In response to the core 52 (i.e., the destination) receiving the controlportion, the core 52 may send an acknowledgment signal (or message)across the interconnect 26 to the core 22 in operation 156. Theacknowledgement signal may pass through the core 52 and pass across theinterconnect 14 to the core 12 in the operation 158.

In response to the core 12 (i.e., the source) receiving theacknowledgement signal, the core 12 sends a data portion of the packetacross the interconnect 14 to the core 22 in operation 160. The dataportion pass through the core 22 and passes across the interconnect 26to the core 52 in operation 162.

In communicating across the multi-core die, each packet may requirethree traversals of signals. These signal traversals may be referred toas a first pipelined stage, a second pipelined stage and a thirdpipelined stage.

The first stage may involve traversal of a control portion (of a packet)from the source to the destination. The second stage may involvetraversal of an acknowledgement signal (or message) back to the sourcefrom the destination to indicate that the data can be sent from thesource. The third stage may involve the sending of a data portion (ofthe packet) to the destination from the source.

The first, second and third pipelined stages may be pipelined to improvethe network throughput such that request packets allocate anacknowledgement channel for a next data clock cycle. The data channelmay be allocated during the data clock cycle following the receipt ofthe acknowledge signal. The three pipeline stages of a router areillustrated in FIG.4.

FIG. 4 shows a router of one core in accordance with an exampleembodiment of the present invention. Other embodiments andconfigurations are also within the scope of the present invention.

More specifically, FIG. 4 shows three pipeline stages of a router,namely a request pipeline stage 200 (or first pipeline stage), anacknowledge pipeline stage 250 (or second pipeline stage) and a transmitpipeline stage 260 (or third pipeline stage). The use of the threepipeline stages may improve throughput over an entirely circuit-switchednetwork while retaining nearly all of energy savings.

As shown in FIG. 4, the request pipeline stage 200 may includeflip-flops 202, 204, 206, multiplexers 203, 205, directional logic 210,a priority encoder 215, a flip-flop 220 and a multiplexer 225.

The packet may be received as an input to the flip-flop 202, to oneinput of the multiplexer 203 and to one input of the multiplexer 205. Anoutput of the flip-flop 202 may be coupled to another input of themultiplexer 203. An output of the multiplexer 203 may be provided to aninput of the flip-flop 204. An output of the flip-flop 204 may be provedto another input of the multiplexer 205. An output of the multiplexer205 may be coupled to an input of flip-flop 206. The flip-flops 202, 204and 206 may receive a packet clock as select signals.

The flip-flops 202, 204 and 206 and the multiplexers 203 and 205 mayserve to buffer received control packets (or received control portions)during a time before a handshake or stop signal can be transmitted backto the transmitter (or source) of these packets indicating that thetransmitter (or source) should stop temporarily due to congestion.Because it may take some time for this signal to reach the transmitter(or source) of the control packets (or control portions), some packetsmay still be received during this time and need to be buffered by theseflip-flops. During normal operation, data may go through the multiplexer205 directly to flip-flop 206 and to the directional logic 210. Thenumber of flip-flop/multiplexer stages may depend on the time it takesthe handshaking signal to reach the previous core relative to the rateat which packets are being transmitted.

An output of the flip-flop 206 may be provided to the directional logic210. The directional logic 210 may compare destination address bits (xand y) of the control portion of the packet to the current core'saddress in order to determine in which direction the packets should betransmitted. In other words, the directional logic 210 may determinedwhich neighbor core will receive the control data. An output of thedirectional logic 210 may be provided to the priority encoder 215.

Additionally, input flip-flops 202, 204 and 206 as well as directionallogic 210 may be provided at each direction input (north, south, eastand west) of the priority encoder 215. The priority encoder 215 mayselect one of the directions that want to transmit its control packet(or control portion) out to each direction and the direction outputsconnect to the corresponding priority encoder inputs of the other threedirections.

Each multiplexer 220 may receive its data from the control packetbuffering from the other three directions and the select may come fromits priority encoder 215. The flip-flops 252 and 262 may store the samemultiplexer selects as used from the multiplexer 220. These selects aregiven to the multiplexers 255 and 265 in successive cycles in order toimplement the pipelining.

In FIG. 4, L, R and S refer to left, right and straight as inputs forthe multiplexers, where the inputs in the request pipeline stage 200 maybe a 6 bit destination address (corresponding to 64 cores), the inputsin the acknowledge pipeline stage 250 may be a single acknowledge bit,and the inputs in the transmit pipeline stage 260 may be a full 512 dataportion. The relative direction of the arrows in FIG. 4 may indicate adirection of data flow (from a source at the left to a destination atthe right, acknowledge back to the source, and data to the destination).This may be independent of the actual direction of flow on a chip whichmay change directions at intermediate nodes (using the L, R and S inputsand outputs).

The priority encoder 215 may determine a priority of the data within therouter in order to determine an order of transmission or processing. Anoutput of the priority encoder 215 may be provided to the multiplexer220, and an output of the multiplexer 220 may be provided to theflip-flop 220, which allows the control data to exit the router.

The request pipeline stage 200 may correspond to a first stage thatinvolves traversal of the control portion of the packet from the sourceto the destination. The request pipeline stage 200 may be considered touse resources of the packet switched network.

The acknowledge pipeline stage 250 relates to the receiving of anacknowledgement signal at a router. As shown in FIG. 4, the acknowledgepipeline stage 250 may include a flip-flop 252 and a multiplexer 255.The acknowledge pipeline stage 250 may operate using a data clock ratherthan a packet clock as in the request pipeline stage 200. Thus, theacknowledge pipeline stage 250 may be considered to use resources of acircuit switched network.

The acknowledge pipeline stage 250 may correspond to the second stage(or second pipeline stage) that involves traversal of theacknowledgement signal back to the source from the destination toindicate that the data can be sent from the source.

The transmit pipeline stage 260 relates to the sending of the dataportion of the packet at the router. The transmit pipeline stage mayinclude flip-flop 262 coupled to a multiplexer 265. The transmitpipeline stage 260 may correspond to the third stage that involves thesending of data to the destination from the source. The transmitpipeline stage 260 may operate using a data clock rather than the packetclock as in the request pipeline stage 200. Thus, the transmit pipelinestage 260 may be considered to use resources of a circuit switchednetwork.

The use of these three pipeline stages may improve the throughput overan entirely circuit-switched network while retaining nearly all of theenergy savings. This is because the routing and flow control is hiddenfrom the data transmit pipeline stage.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to effect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

1. A method of communicating across a multi-core die, the methodcomprising: sending a control portion of a packet from a first core,through a second core to a third core using resources of a packetswitched network, the first core being a source and the third core beinga destination; sending an acknowledgment signal from the third core tothe first core in response to the third core receiving the controlportion; and sending a data portion of the packet from the first corethrough the second core and to the third core using resources of acircuit switched network in response to the first core receiving theacknowledgement signal.
 2. The method of claim 1, wherein the controlportion is sent from the first core to the second core using resourcesof the packet switched network.
 3. The method of claim 1, wherein theacknowledgement signal is sent from the third core through the secondcore and to the first core using resources of the circuit switchednetwork.
 4. The method of claim 1, wherein the data portion is sent fromthe first core to the second core using resources of the circuitswitched network.
 5. The method of claim 1, wherein the control portioncontains a destination address.
 6. The method of claim 1, whereinsending the control portion from the first core to the second coreincludes sending the control portion along an interconnect of the diebetween the first core and the second core.
 7. The method of claim 6,wherein sending the data portion from the first core to the second coreincludes sending the data portion along the interconnect of the diebetween the first core and the second core.
 8. The method of claim 6,further comprising allocating the interconnect between the first coreand the second core for the data portion of the packet in response tothe second core receiving the control portion from the first core. 9.The method of claim 1, wherein a link between the first core and thesecond core is dedicated upon the control portion being received at thesecond core from the first core.
 10. A die comprising: a first core, asecond core and a third core; a first interconnect between the firstcore and the second core; and a second interconnect between the secondcore and the third core, and the first, second and third cores tocommunicate across the die using resources of a packet switched networkwhen sending a control portion of a packet across the die, and thefirst, second and third cores to communicate using resources of acircuit switched network when sending a data portion of the packetacross the die.
 11. The die of claim 10, wherein the first core to sendthe control portion of the packet through the second core to the thirdcore using the resources of the packet switched network.
 12. The die ofclaim 10, wherein the first interconnect between the first core and thesecond core is to be allocated for the data portion of the packet inresponse to the second core receiving the control portion from the firstcore.
 13. The die of claim 10, wherein the third core to send anacknowledgement signal through the second core and to the first coreusing the resources of the circuit switched network in response to thethird core receiving the control portion.
 14. The die of claim 10,wherein the first core to send the data portion through the second coreand to the third core using the resources of the circuit switchednetwork.
 15. The die of claim 10, wherein different clocks are to beused to synchronize resources of the packet switched network and thecircuit switched network.